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  "body": "\n## Summary\n\nA **perfect ruler** of length $\\ell$ is a ruler with [[integer|0C4JS9RF5M]] markings $a_1=0 \u003c a_2 \u003c \\dots \u003c a_n=\\ell$, for which there exists an integer $m$ such that any positive integer $k\\leq m$ is uniquely expressed as the difference $k=a_i-a_j$ for some $i,j$. This is referred to as an $m$-perfect ruler.\n",
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